Explosives



United States Patent 3,177,102 EXPLOSIVES Joseph R. Hradel, MountPleasant, Mich, assignor to The Dow Chemical Company, Midland, Mich, acorporation of Delaware No Drawing. Filed Jan. 7, 1963, Ser. No. 249,5872 Claims. (Cl. 149-43) The present invention relates to a method ofpreparing explosive compositions from insensitive components. Morespecifically, the present invention involves reacting a relativelyinsensitive oxidizer with a fuel for a period of time at ambienttemperature during Which time the admixture undergoes auto-reactionthereby yielding a sensitive explosive composition.

This application is a continuation-in-part of my copending applicationSerial No. 48,820, filed August 11, 1960, now abandoned. This latterapplication in turn is a continuation-in-part of my copendingapplications Serial No. 807,406, filed on April 20, 1959, now abandoned,and Serial No. 763,908, filed on September 29, 1958, now abandoned.

It is the principal object of the present invention to provide a methodof preparing explosive compositions containing an oxidizing salt and afuel which are initially relatively insensitive. 7

It is a further object of the present invention to provide a processwhereby initially insensitive explosive compositions after mixing,undergo auto-reaction, thereby yielding sensitive explosivecompositions.

Another object of the present invention is to provide a method ofpreparing explosive compositions in which the oxidizing salt, e.g.,ammonium nitrate, may be present initially in solution form, as in anaqueous or aqueous ammoniacal solution.

An additional object of the present invention is to provide a method ofpreparing a substantially insensitive initial explosive compositionhaving an oxidizer .in solution form which oxidizer is capable ofundergoing reaction with metals and other fuels, and thereby form anovel, sensitive explosive. composition possessing high explosivestrength.

Still another object of the present invention is to provide sensitiveexplosive compositions that, upon detonation, are substantially devoidof toxic gases, such as carbon monoxide, carbon dioxide, and the noxiousoxides of nitrogen, which toxic materials constitute serious healthhazards.

These and other objects and advantages of the present invention will beapparentto those skilled in the art to which these inventions pertain.

In carrying out the process of the present invention, unexpectedly ithas been found that upon admixing ammonium nitrate with a metal fuel,e.g., a particulate light metal component containing reactive amounts ofmagnesium, in the presence of a liquid which solubilizes ordisassociates the oxidizer, said fuel being capable of undergoingcorrosive action with the so-wetted or solubilized oxidizer, over aperiod of time provides a sensitive explosive composition.

In a preferred embodiment of the present invention, an admixture ofammonium nitrate with certain light metals is prepared. This initialmixture, contrary to the BJJKWZ Patented Apr. 6, 1965 teaching of theprior art, is an explosive composition that is substantiallyinsensitive.

However, upon passage of time at ambient temperature, the insensitiveexplosive composition undergoes selfor auto-chemical reaction to formsubstantially solid, sensitive explosive compositions. Thesecompositions have been demonstrated to possess unexpectedly highexplosive strength not exhibited by prior art ammonium nitrateexplosives. These novel sensitive explosive compositions, whendetonated, produce much sharper movement of rock or material beingtreated, higher percussion or brisance and more intense shock waves thanother ammonium nitrate explosive compositions.

The initial substantially insensitive compositions comprise generally aliquid solution of ammonium nitrate in which the solvent is selectedfrom the group consisting of liquid ammonia, water and ammoniumhydroxide, and a light metal thermal carrier, preferably selected fromthe group consisting of magnesium, magnesium alloys, magnesium-aluminumalloys and mixtures thereof which contain reactive amounts of magnesium.

Novel methods for the production at the situs of or in a bore holeitself of the sensitive explosive composition have been found. Thesecomprise for example, the positioning of an ammoniacal solution ofammonium nitrate (about 50-75 percent NH NO, 5-15 percent water and20-35 percent NH on a weight basis) in a bore hole in admixture with alight metal thermal carrier as defined heretofore, and interacting theresulting admixture at the ambient bore hole temperature untilsubstantial exothermal activity resulting from said interaction hasoccurred. Such methods produce sensitive compositions, or reactionproducts, that are detonated preferably at the peak of the exothermalactivity, or after this peak has been passed, to provide explosion withvery high power factors.

In preparing the initial insensitive explosive compositions utilizingthe ammoniacal ammonium nitrate solution, it is of course, mosteconomical to admix the ammoniacal ammonium nitrate solutions with thelight metal thermal'carrier or fuel at the site of use. The commerciallyavailable ammonium nitrate solutions are easy to transport, whilemaintaining a good safety margin above many conventional high explosivecompounds. The metal is also conveniently transported to the site of usewhere the admixing of the oxidizer and fuel components is readilycarried out. This mixing may be done above ground since the resultingadmixture is initially insensitive, or it may be carried out at thebottom of the well or bore hole to be treated. In some instances, themetal carrier may be positioned at the bottom of the bore hole first andthe ammoniacal ammonium nitrate solution poured over it. The procedurecan be reversed. The precise procedure to be followed will depend uponthe nature of the explosive operation to be conducted.

In situations wherein loss of either oxidizer or fuel may occur uponmixing, for example in holes containing fissures or in water filledholes, the fuel and oxidizer may be introduced into a waterproof orleakproof container. It is to be understood that the container may firstbe inserted into the 'hole to be filled with explosive and the fuel andoxidizer then added thereto. Alternatively, the explosive mix componentscan be placed into the container and the so-filled holder then beinserted into the bore hole.

In addition to the exemplary compositions presented above, which havebeen cited to illustrate the method of the invention, I have found manyother explosive compositions which are initially substantiallyinsensitive, but which can be made to undergo autoreaction orinteraction upon passage of time at ambient or bore hole temperatureconditions to form, upon corrosion, sensitive reaction products. Thismethod thereby provides an exceedingly safe explosive system.

Further, sensitive explosive compositions have been prepared wherein theoxidizing ammonium nitrate salt may be in substantially granular orpowdered form, semifiuid mixture, and complete solution mixtures, asdisclosed in this application. As long as there is suflicient water orother ionizing media present, even initially insensitive compositionsthat are substantially dry to the touch can be made to undergo reactionto form sensitive corrosion reaction products.

The actual time necessary to accomplish the desired interaction of themix components will vary depending upon the type of oxidizer, fuelutilized and amount of dissociation solvent present in the composition.However, in any event, substantially complete sensitization reactionnormally is obtained within a period of time ranging from about /2 hourto about 48 hours. For example, with a composition of about 60 partsaqueous ammoniacal ammonium nitrate (25 percent NH 6 percent H and 69percent NH NO and 40 parts of a 50-50 mixture of substantially pureparticulated magnesium and aluminum of greater than about 20 mesh U.S.standard sieve, essentially complete reaction is obtained within aperiod of from about 4 to about 8 hours. Similar reaction periods arefound for such compositions of ammonium nitrate solution and thesemetals wherein the metal can vary from about 4-65 percent by weight andthe solution from about 96 to about 35 percent by weight on thecomposition. On the other hand, if the aluminum content of the binarymetal mixture in such compositions is increased, a correspondingincrease in curing time is indicated. If more finely divided metals areutilized, or if more corrosion sensitive metals are used, theautogenetic reaction is found to take place in a shortened period oftime, i.e., from about to about 2-3 hours.

Additionally with an ammonium nitrate explosive composition containingfrom about 2 to about 10 percent of granular 20-80 mesh magnesium or amagnesium alloy, such as ASTM designated ZKlO, ZK60, or A33 for exampleand from about 1 to about 6 percent water, the balance by weight beingprilled fertilizer grade ammonium nitrate, the reaction is found to becompleted in about 4-5 hours.

For compositions that remain substantially in granular form, but whichare slightly wetted with such liquid solvents, reaction periods lastingfrom several hours to as much as several days in some instances havebeen found.

These findings have enabled me to work with and prepare manycompositions that are initially safe to handle but which undergointeraction or auto-reaction under ambient conditions to form sensitizedexplosives. In many instances, exothermal auto-reactions that are nor-.mally quite slow have been speeded up by external application of heat orby application of additional liquid solvents.

Detonation of the resulting explosive mixes conveniently is carried outby means of a shaped charge, Tetryl, RDX, cast pentolite or otherboosters of similar power factors.

The deton-ator ordinarily will be selected from those which arethennally stable against detonation to temperatures higher than thatencountered in the interaction of the mix components.

In practice, the detonating booster, fitted with a nonarmed firing cord,or fuse type firing line ordinarily is placed in contact with the mix orwithin the mix proper. In the latter case, the booster will be placed ina bore hole along with the composition ingredients prior to theautogenetic reaction, while in the former case the booster may beinserted into the hole either prior to or after the desired mixreaction. The booster then can be armed by connection into aconventional firing device just prior to the time of detonation.

Compositions of the present invention may be utilized for a wide varietyof applications in oil well and mining operations, for example, oil wellrecovery processes, hard rock mining, quarrying, construction, wastedisposal wells, and in porous rock blasting. The novel methods of thepresent invention have utility in the preparation of the explosivecompositions at the general situs of a bore hole itself and in thedirect area of intended use. However, if desired the reaction of the mixcomponents can be carried out in a suitable container and the resultingsolid explosive be stored and transported, using conventional explosivesafety practices, to blast sites and utilized in much the same manner asother sensitive prepackaged explosives.

The following examples will serve to further illustrate the invention,but are not meant to limit it thereto.

EXAMPLE 1 Thermal profiles measuring exothermal activity of autosreaction iof explosive composition upon passage of time to formsensitive explosive reaction product In order to determine the amount ofexothermal activity resulting from the autogenetic or self-reactionoccurring in an initially insensitive explosive admixture upon passageof time, an extensive series of thermal profiles; was prepared.Illustrative thermal profiles are set forth below in Graph I.

In this series, the rise in temperature above ambient upon passage oftime was measured by recording thermometer means. Also the role of wateror other ionizing medium was ascertained.

Load number A was prepared from 72 percent by weight of an ammoniacalammonium nitrate solution (formed from 69.8 parts of ammonium nitrate,23.8 parts of liquid ammonia and 6.4 parts of water), and 28 percent byweight of mixed metal. Equal parts (14 percent each) of magnesium bandsaw chips and aluminum band saw chips were utilized. It is seen that thetemperature of the test load was raised exothermally from ambienttemperature of 20 F. to a maximum of about F., at which higher point theload solidified, indicating that the desired sensitive explosivereaction product had been formed. Thereafter, the temperature of thesystem gradually subsided.

Test load B contained 72 percent of the same liquid ammoniacal ammoniumnitrate solution as used for load A together with 14 percent by weighteach of coarse magnesium mill chips and aluminum bars approximately /8inch by A inch by inch in configuration. Peak exotherm activity wasobserved at F. after about four and one-half hours passage of time. Therole of the coarser metal particles in causing lengthening of theauto-reaction period was confirmed, these mixed metal particles of thisload being substantially coarser than the mixed metals of test load A.

Test load C as initially prepared was identical to test load B. However,as the exothermal activity decreased noticeably after about six andone-half hours, a small amount of water was added. Within one andone-half hours later the exothermal reaction was again observed toliberate substantial quantities of heat with a new exotherm peak beingreached at about 137 F., the reaction thereafter subsiding. From thesedata, it is suggested that the reaction is ionic and that the waterpresent becomes chemically bound, perhaps in a manner discussed later inthis specification.

5 pound explosive test load was formed by dissolving three pounds offertilizer grade ammonium nitrate prillsin one pound of liquid anhydrousammonia. The

,resulting ammoniacal ammonium nitrate solution was admixed with 1.5pounds of mixed metal, formed from a fifty-fifty ratio of magnesiumlathe s havings to aluminum shop scrap chips. .A six inch diameter bysix foot deep bore hole was made in the ground in the test area. The

load was placed in the hole. Within forty minutes after the initialadmixture wasplacedin the bore hole, exothermal activity was noted.Three hours later, the reaction was proceeding vigorously and the loadsolidified approximately four and one-half hours after being placed inthe bore hole. A shaped charge then was placed on top of the load andthe hole tamped with about five feet of sand. Forty-eight hoursfollowing solidification, the test load was fired electrically usingtheshaped charge.

The resulting blast produced a crater approximately 3-5 .feet indiameter.

Following the procedure of. Example 2 a similar ar'n monium nitratesolution wasprepared. Three percent water was added based on the weightof the total charge and this solution was then admixed with the mixedmetal carrier as used in Example" 2. The solution solidified in threeand one-half hours and was permitted to stand forty-eight hours beforefiring. The load was successfully fired, A crater about six feet indiameter was formed.

. EXAMPLE'4 Three and one-half pounds of a nearly saturated solution ofammonium nitrate in water, was admixed with 1.5 pounds of magnesium bandsaw chips and the resulting admixture placed in the bore hole. Peakexothermal activity occurred in a shorter period of time than wasobserved in Examples 24 inclusive. The load was fired successfullyforty-eight hours later with a crater about six feetin diameter beingproduced.

Heretofore, the ammonium nitrate explosions have been regarded generallyas slower detonating reactions, based primarily upon the volume of gasesliberated. In distinct contrast, the test loads of the presentinvention, as illustrated in the above examples, provide a quick, sharpreaction accompanied by high percussion and brisance and by intenseshock waves.

The enhanced power factor resulting from the detonation of thecompositions of the present invention seems to be derived primarily fromthe intense heat generated and only secondarily from the initialliberation of more gases. The effect of the extremely high heats thatare generated is, of course, to increase tremendously the volume of gasmade available, in accord with the normal gas volume-temperaturerelationships. This results in greater power since the rock breakage,for example, as observed in the blasting of taconite ore with thesenovel, reacted compositions is in the order of thirty-five tons perpound of initial insensitive explosive load as against twenty tons perpound of load wherein non-reacted, metal-containing dry and semi-fluidammonium nitrate loads have been detonated by me.

While the above examples illustrate the unexpected power factorexhibited by the reacted or aged explosive compositions of the presentinvention, other observations have been made that are helpful indetermining the nature' of the complex reactions occurring in thesesystems.

The initially substantially insensitive explosive compo sition undergoesauto-reaction chemically, as evidenced by the strong exotherms recordedin the experiments conducted under Example 1 above. There is someindication that'when magnesium is present that the following reactionoccurs in the presence of water:

At the same time, there is evidence that the magnesium for example, maybe undergoing reaction with the am monium nitrate to form magnesiumnitrate, the water present being taken up perhaps as the hexahydrate ofthe resulting salt, or the dihydrate, forexample, in accord with thefollowing reaction:

This is supported by the above data which indicate that when theexothermal reaction tapers off, it can be initiated again by adding asmall quantity of water to the charge. Further, when the auto-reactionhas been completed, usually within twenty-four hours, the completedreaction product has been observed to be substantially in solid form.Usually after about five hours with the above described mixes,sufiicient exothermal activity has occurred so that the resultingreaction products can be detonated successfully. Close examinationreveals that while much of the elemental metal thermal carriers or fuelsare still present as such, a very substantial portion has been convertedto a metal salt or a group of salts. Such reaction product has beenremoved from the bore hole, permitted to remain at ambient temperaturefor several days, returned to the bore hole and detonated by shapedcharges'as a completely dry, granular explosive.

After the mixture is placed in a bore hole, there is frequently a lag intime of up to as much as one or more hours before any appreciableexothermal activity is observed when using coarse metal particles. Thespeed of V the reaction and, hence, the quantity of exotherm produced,can be controlled appropriately by regulating the particle size andconfiguration of the metal carrier and by controlling the amount ofwater or other oxidizer dissociation solvent present in the initialinsensitive explosive composition. increasing the amount of water, tendsto speed up the reaction. It has been found that the auto-reaction canbe made sufliciently violent so as to actually throw the material out ofthe bore hole. Experimentation has produced the operable limits, as setout above in this specification, for controlling these factors.

Generally, the auto-reaction is completed within twentyfour hoursalthough it is generally preferred to detonate Decreasing the particlesize and- 7 the reaction product while the exothermal activity of thesystem is at or near its peak.

Experimental evidence points towards the possibility that with highermetal loads, vaporization of magnesium uses substantially all of theoxygen present and liberated. This is accomplished by a tremendous risein heat, the magnesium being vaporized primarily as magnesium oxide. Thelight colored magnesium oxide vapor has been carefully observed in smalltest shots. No residual magnesium is observed, even when the theoreticalmaximum amount of thermal carrier based on magnesiumoxygen mixstoichiometry is present. Thus, the magnesium, not already involved inthe auto-reaction product, serves as the fuel, producing intense heatthat raises the temperature of aluminum, if present for example inadmixture with or alloyed with the reactive magnesium, which has ahigher ignition point than magnesium, to its boiling or vaporizingpoint, causing it to probably undergo the following reaction:

2Al+N =2AlN+262.8 K-calories per mole This reaction occurs attemperatures in the area of about 32503500 degrees Fahrenheit, with theresulting tremendous amount of heat being liberated. The lcalorie valuemore than overcomes any loss of gaseous nitrogen. This excessive heat,together with its effect on the volume of gas liberated in thedetonation, may be largely responsible for the unusually high powerfactor obtained with the explosives of the present invention. Evidencepoints toward the reaction forming an aluminum nitride rather than theformation of an aluminum oxide, and as such precludes the formation ofnoxious oxides of nitrogen which heretofore constituted a safety hazardin the muck or rubble remaining upon detonation of conventional ammoniumnitrate explosives.

Frequently, conventional ammonium nitrate explosions result insubstantial residual amounts of ammonia, readily evidenced by theammonia smell. With the explosive compositions of the present invention,no residual ammonia odor is present upon detonation, the ammonia beingcompletely converted to nitrogen and hydrogen at the high temperaturesinvolved in the reaction system.

There is also evidence that substantial amounts of hydrogen are madeavailable during the explosion reaction and that these also play animportant role in the superior performance observed. For example, intest shots in the field, following detonation, a characteristic bluishflame has been observed in cracks and fissures in the rock opened up bythe blast in which oxygen is apparently reacting with the residualhydrogen, as secondary explosives.

The tremendous power factor achieved by the explosive compositions ofthe present invention has made it possible to accomplish many blastingoperations with a very small amount of explosive as compared withconventional ammonium nitrate explosives.

Various modifications can be made in the process of the presentinvention without departing from the spirit or scope thereof for it isto be understood that the invention is limited only as defined in theappended claims.

I claim:

1. A method for preparing a sensitive solidified explosive compositionfrom insensitive components which comprises; admixing from about 96 toabout 35 parts by weight of a solution of ammonium nitrate with about 4to about parts by weight of a light metal fuel selected from the groupconsisting of magnesium, magnesium alloys, admixtures of magnesium andaluminum and mixtures thereof, said light metal fuel further beingcharacterized in having at least about 50 Weight percent magnesiumcontent, said solution containing at least about 50 weight percentammonium nitrate, and the solvent for said ammonium nitrate being amember selected from the group consisting of water, ammonia and ammoniumhydroxide, said light metal fuel being capable of undergoing chemicalreaction With said ammonium nitrate solution, and, reacting saidsolution and said metal fuel at ambient temperature for a period of timeof from about /2 to about 24 hours thereby to provide a sensitivesolidified explosive composition.

2. A method of preparing a sensitive solidified explosive compositionfrom insensitive components which comprises;

(a) admixing from about 96 to about 35 parts of an ammoniacal solutionof ammonium nitrate with from about 4 to about 65 parts of a light metalthermal carrier, said ammoniacal solution of ammonium nitrate containingfrom about 5 to about 15 percent Water and from about 20 to about 35percent ammonia, said light metal thermal carrier being selected fromthe group consisting of magnesium, magnesium alloys, admixtures ofmagnesium and aluminum and mixtures thereof, said light metal thermalcarrier being further characterized in having at least about 50 weightpercent magnesium content, and, interacting the resulting admixture atambient temperature until peak exothermal activity'resulting from theinteraction has occurred and the admixture has solidified.

References Cited by the Examiner UNITED STATES PATENTS 2,836,481 5/58Strenge et al. 149-42 2,903,969 9/59 Kolbe 149-46 2,978,864 4/61 Stengel149-1 X 2,992,086 7/61 Porter 149-43 3,034,874 5/62 Emmons 149-41 X3,094,443 6/63 Hr-adel et al. 149-1 CARL D. QUARFORTH, Primary Examiner.

L. D. ROSDOL, Examiner.

1. A METHOD FOR PREPARING A SENSITIVE SOLIDIFIED EXPLOSIVE COMPOSITIONFROM INSENSITIVE COMPONENTS WHICH COMPRISES; ADMIXING FROM ABOUT 96 TOABOUT 35 PARTS BY WEIGHT OF A SOLUTION OF AMMONIUM NITRATE WITH ABOUT 4TO ABOUT 65 PARTS BY WEIGHT OF A LIGHT METAL FUEL SELECTED FROM THEGROUP CONSISTING OF MAGNESIUM, MAGNESIUM ALLOYS, ADMIXTURES OF MAGNESIUMAND ALUMINUM AND MIXTURES THEREOF, SAID LIGHT METAL FUEL FURTHER BEINGCHARACTERIZED IN HAVING AT LEAST ABOUT 50 WEIGHT PERCENT MAGNESIUMCONTENT, SAID SOLUTION CONTAINING AT LEAST ABOUT 50 WEIGHT PERCENTAMMONIUM NITRATE, AND THE SOLVENT FOR SAID AMMONIUM NITRATE BEING AMEMBER SELECTED FROM THE GROUP CONSISTING OF WATER, AMMONIA AND AMMONIUMHYDROXIDE, SAID LIGHT METAL FUEL BEING CAPABLE OF UNDERGOING CHEMICALREACTION WITH SAID AMMONIUM NITRATE SOLUTION, AND, REACTING SAIDSOLUTION AND SAID METAL FUEL AT AMBIENT TEMPERATURE FOR A PERIOD OF TIMEOF FROM ABOUT 1/2 TO ABOUT 24 HOURS THEREBY TO PROVIDE A SENSITIVESOLIDIFIED EXPLOSIVE COMPOSITION.